1. Technical Field of the Invention
The present invention relates to a cleaning method and a cleaning apparatus for objects to be cleaned such as components that has recess structures or more concretely components formed by machining, press processing, or the like and particularly precision machined components to be used for electronics components and so on.
2. Description of the Related Art
Conventionally, there have been three indispensable processes of “cleaning”, “rinsing”, and “drying” for the components formed by machining, press processing, or the like and particularly the precision machined components to be used for electronics components after the process machining, press processing, or the like. This is because a processing oil is used for the object to be processed during machining or press processing and the unnecessary processing oil that adheres to this object to be processed is required to be removed. Particularly, in the case of a precision component that needs an advanced cleaning effect, there is also demanded a cleaning agent of high cleaning capability, and extreme importance is attached to the drying process that is the final process.
On the background as described above, the lubricating oil, or the processing oil has been removed by using vapor cleaning with flon 113 or 1,1,1-trichloroethane in the final process of the precision cleaning field. However, the flon 113 and 1,1,1-trichloroethane have caused the destruction of the ozone layer in environmental terms, and the 1,1,1-trichloroethane has largely influenced the human central nervous system and caused unconsciousness and respiratory arrest at a high density. For the above reasons, the fluorine regulation has started in July 1989 in Japan, and the production of flon was totally abolished in 1995.
In accordance with the abolition of flon 113 and 1,1,1-trichloroethane, there are recently used liquid cleaning agents, which substitute for the ozone destruction substances and exemplified by nonaqueous systems of bromine based solvents (1-bromopropane and propyl promide), hydrocarbon based solvents (normal paraffin system, isoparaffin system, naphthenic system, and aromatic system), iodine based solvents (perfluoro-n-propyl iodide, perfluoro-n-butyl iodide, and perfluoro-n-hexyl iodide), chlorine based solvents (aliphatic group of trichloroethylene, tetrachloroethylene, methylene chloride, and trans-1,2-dichloroethylene, aromatic group of monochlorotoluene, benzotrifluoride, parachloro-benzotrifluoride (PCBTF), and 3,4-dichloro benzotrifluoride (3,4-DCBTF)), fluorine based solvents (HCFC system of HCFC-255ca, HCFC-141b, and HCFC-123, HFC system of HFC-4310mee, HFC-356mcf, and HFC-338Pcc, HFE system of HFE-7100 and HFE-7200, and cyclic HFC system of OFCPA), siloxane based solvents (volatile methylsiloxane system (VMS), dodecamethylcyclohexasiloxane, hexamethyldisiloxane, decamethyltetrasiloxane), ketone based solvents (methyl ethyl ketone (MEX)), and alcohol based solvents (ethanol, isopropanol (IPA), or pentafluoropropanol (5FP)).
As quasi-water systems, there are used hydrocarbon systems (normal paraffin system, isoparaffin system, naphthenic system, or aromatic group), glycol ethers (ethylene based glycol ether or isoprene based glycol ether), N-methyl-2-pyrrolidone (NMP), terbenzene (d-limonene), or siloxane systems (volatile methylsiloxane system: VMS, dodecamethylcyclohexane, hexamethyldisiloxane, or decamethyltetrasiloxane).
As water systems, there are enumerated additive-free water (deoxygenated water, deionized water, or ultrapure water), cleaning property-improved water with additive (alkaline system, acid system, ionic surface active agent, nonionic surface active agent, higher alcohol based surface active agent, or ozone-added ultrapure water), and so on.
As described above, numbers of liquid cleaning agents for substituting flon are produced, and cleaning methods using them are used for precision components.
As disclosed in Japanese unexamined patent publication No. H09-263994 of a battery casing, there is used cleaning for burning out the lubricating oil, or the processing oil by carrying out annealing at a very high temperature of 700 to 900° C. instead of the organic solvent. However, in the case of an aluminum sheet for film lamination used for aluminum electrolytic capacitors, dirt of rolling oil, metal powders, and so on left on the rolled sheet surface is burnt onto the surface during annealing, and this causes troubles of defective appearance, defective adhesion, and so on. Therefore, according to Japanese unexamined patent publication No. H06-272015 of annealing in a softening process, the annealing process is carried out after cleaning the surface of the aluminum sheet with mineral acid or organic acid or the mixed acid of them.
Moreover, according to the international publication Nos. WO97/42668, WO97/42667 and WO98/10475, as a battery casing, there is recently used a surface treated steel sheet obtained by degreasing a steel sheet by using an organic solvent or an alkaline based degreasing agent, subjecting the sheet to cleaning with acid, plating, and postheating treatment, heating the sheet to the melting point of a petroleum wax based lubricant to be coated and using the surface treated steel sheet on the surface of which the molten lubricant has been coated for deep drawing processing, DI (Drawn & Ironed) processing or DS (Dry Sanding) processing, and DTR (Drawing & Thin Redrawing) processing. The greater part of this lubricating oil can be simplify vaporized and removed if heating is carried out at a temperature of 200 to 350° C. after the processing and molding, and therefore, the cleaning after the processing can be simplified.
Furthermore, in the case of the casing of the HDD (Hard Disk Drive), electrolytic capacitors, precision electronic components, and so on described in Japanese Patent No. 3234541, an organic resin film, which contains a lubricant on one surface or both surfaces of an aluminum alloy material, is formed to improve the molding processability, a volatile lubricant is coated on its surface and the lubricant is vaporized and removed by heating after the processing.
As another cleaning method, as disclosed in Japanese unexamined patent publication No. 2000-225382, it is proposed to change the state of the metal mold surface with coexisting organic or inorganic reducing agent that operates as a cleaning element and to clean and remove dirt without damage caused by an object put in contact when cleaning metal components and the metal mold with water in a supercritical or subcritical state. Moreover, Japanese publicized Japanese translation of PCT international application No. 59-502137 proposes a cleaning method for removing organic matters by using a supercritical gas. Moreover, Japanese patent No. 2832190 discloses a method for improving the cleaning effect by rapidly changing the state of the fluid in a supercritical or subcritical state.
As described above, the lubricating oil for improving the molding processability is indispensable for molding processing, and it is no exaggeration to say that the development of a lubricating oil is worthy of the development of more advanced molding processing. However, the lubricating oil used for this molding processing causes defective products due to the deterioration of product performances, contamination, and so on unless the oil is completely removed when the processed precision components are used as products. Therefore, it is also indispensable to develop a cleaning method for completely removing this lubricating oil similarly to coating of the lubricating oil during the molding processing.
However, the substitute flons (chlorofluorocarbons) are often used as solvents that exert no influence on the destruction of the ozone layer considering the environmental factors with regard to the cleaning method using a solvent and particularly to degreasing, whereas the influences on the environment have been discovered a little. For example, 2-bromopropane is an existing material that has been used as an intermediate of pharmaceuticals, agricultural chemicals, and photosensitizers, an alkylating agent, and so on. Moreover, the time and cost necessary for cleaning becomes a serious problem. A cleaning level after processing is determined depending on what kind of product the molded component is used for. Therefore, it is desirable to use a solvent of high detergency, whereas the influences of the solvent of high detergency exerting on the environment are unknown as described above. Therefore, since the solvent that exerts a little influence also has a low detergency, the time and processes (cleaning frequency) must also be increased.
For example, precision cleaning is necessary for the components that are plated after processing like battery casings and aluminum electrolytic capacitors, and a long time is necessary for carrying out the cleaning process to carry out degreasing, impurity removal, and activation. Moreover, prevention of degassing during use is important for the casings used for HDD's and so on, and importance is attached to the degreasing process. Moreover, in a case of solvent cleaning, handling is very complicated with regard to the management factors of solvent management (Fire Protection Law), human treatment (Occupational Health and Safety Law), waste fluid recovery and so on, and much labor have been required for them, consequently reducing the productive efficiency.
Accordingly, there has been the growing trend of using a method for evaporating the volatile lubricating oil through annealing after the processing by a combination of an organic resin coating and a volatile lubricating oil as a method for simplifying the cleaning method of using a solvent as far as possible or a method dispensable with cleaning with solvent. However, this method is, of course, not able to completely evaporate the lubricating oil, and oil contents, impurities and so on disadvantageously slightly remain by all means on the processed surface on the microscopic level. Moreover, particularly in the case of deep drawing components that have undergone press molding, components that have complicated structures of recess portions and so on, it is often the case where the lubricating oil is incompletely evaporated due to the structural factors and the case where the lubricating oil for pressing is rubbed into the grain boundaries and so on of stainless steel or the like and impurities remain even when the components are annealed for evaporating the lubricating oil. When the annealing has been carried out in a state in which the residues of oil contents, impurities and so on exist even a little, the oil contents have been carbonized or the impurities have become burnt, consequently causing reductions in the performance of the application products due to defects ascribed to stains and nonuniformity and degassing. Furthermore, the surface treated steel sheet, which is used for the purpose of simplifying the cleaning after the processing or preventing the reduction in the performance of the products even when precision cleaning is not carried out, is subjected to degreasing by means, of an organic solvent or an alkaline based degreasing agent, cleaning with acid, plating, and postheating treatment similarly to the conventional case in the manufacturing processes of the surface treated steel sheet. Therefore, the difference resides only between the cleaning carried out before the processing and the cleaning carried out after the processing, and the influences on the environment and the human beings are scarcely improved.
As another cleaning method considering the environmental factors, there is proposed a cleaning method for carrying out cleaning by means of carbon dioxide or water in a supercritical or subcritical state. This method is merely applied to precision metal molds and peripheral components of the metal mold of a plastic mold lens prism and so on that attach importance to making an organic or inorganic reducing agent that operates as a cleaning element coexist with carbon dioxide or water in the supercritical or subcritical state and carrying out cleaning causing neither the change in the surface state of the metal mold nor damages due to objects put in contact, and mainly intended to remove organic matters.
However, with regard to the components processed by press molding, in particular, electronic components, it has often been the case where the impurities generated during the molding processing are not only the organic matters represented by the lubricating oil but also single bodies of the inorganic matters of swarf, powders, and so on and mixtures of organic matters and inorganic matters, and it has been difficult to obtain an effect of removing the organic matters in an environment in which the organic matters and the inorganic matters coexist even when there is the effect of removing the organic matter.
Moreover, the cleaning system has been very expensive, and much time has been necessary for the cleaning. Therefore, the objects to be cleaned have been mainly the components of metal molds and so on, which have been very expensive and repetitively used.
Accordingly, the object of the present invention is to solve the aforementioned issues and provide a cleaning method and cleaning apparatus of an object to be cleaned such as a component that has a recess structure, capable of improving the cleaning effect by cleaning the object to be cleaned such as the component that has the recess structure by means of a cleaning medium of a liquefied gas or a supercritical fluid.